Achieving long-life and efficient sodium storage through encapsulating Fe3Se4 nanoparticles within hollow mesoporous carbon nanospheres

The application of Fe3Se4 in sodium-ion batteries is limited due to its poor cycling performance and inferior rate capability. Herein, we employ a multi-step process, involving solution adsorption, molten adsorption, calcination and gaseous selenization, to encapsulate Fe3Se4 nanoparticles within monodispersed hollow mesoporous carbon nanospheres (Fe3Se4@HMCN). The space-confined effect of HMCNs refines Fe3Se4 nanoparticles, compelling Fe3Se4 to adhere to the internal wall of HMCNs. In half-cells, Fe3Se4@HMCN exhibits remarkable rate capability at current densities of 0.1–10 A g−1, and exceptional cycling performance (525 mAh g−1 at 1.0 A g−1 after 400 cycles, 282 mAh g−1 at 5.0 A g−1 after 1800 cycles, 204 mAh g−1 after 2000 cycles at 10.0 A g−1), surpassing both pure HMCNs and bare Fe3Se4. The composite structure significantly improves Na storage performance of Fe3Se4, while Fe3Se4 also contributes the majority of the capacity of the composite. Kinetic studies further unveil rapid Na+ transport, low reaction impedance and a predominant pseudocapacitive effect. In Fe3Se4@HMCN//Na3V2(PO4)3 full cell, Fe3Se4@HMCN sustains a discharge capacity of 175 mAh g−1 after 1200 cycles at 5.0 A g−1. The superior electrochemical performance is attributed to the nanoencapsulation structure based on HMCNs, which synergistically enhances electron conduction, ion transport and structural stability of Fe3Se4.